Question

NB：我刚才问了一个问题（How to select from the db where version field is the recent one）并且它运作良好。这不是重复。

SELECT p.* FROM `pricing` p 
JOIN (SELECT `distributor`,MAX(`version`) AS ver 
      FROM `pricing` GROUP BY `distributor`) mx 
  ON mx.ver=p.version AND p.distributor = mx.distributor

使用上述查询，我可以从定价表中选择所有详细信息，其中分销商拥有最新版本。[分销商将有不同的版本。我只需要选择最新版本]。我有另一个名为product_picker的表。我只需要从定价表中选择数据，其中定价代码= product_picker的代码。我使用了以下代码：

SELECT p.* FROM `pricing` p,pk.* 
FROM `product_picker` 
JOIN (SELECT `distributor`,MAX(`version`) AS ver 
      FROM `pricing` GROUP BY `distributor`) mx 
  ON mx.ver=p.version AND p.distributor = mx.distributor 
INNER JOIN `product_picker` pk ON p.code=pk.code

但我知道这不会很好。我刚刚学习了JOIN条款。如何改进我的代码？

谢谢！

Answer 1

机制非常简单：

SELECT p.*, pk.*
FROM 
    `pricing` p 
        JOIN (
            SELECT 
                `distributor`,
                MAX(`version`) AS ver 
            FROM `pricing` 
            GROUP BY `distributor`
        ) mx ON mx.ver = p.version AND p.distributor = mx.distributor
        JOIN `product_picker` pk ON pk.code = p.code -- the join has to be added after the other one, and the ON clause has to make it clear for SQL that the code is the criteria

JOIN和INNER JOIN查询

1 个答案: